This invention relates generally to machine tools having head stocks rotatably supporting main spindles with chucks and tool heads for holding and feeding machining tools relative to workpieces held by the chucks. More particularly, the invention relates to a machine tool having two main spindles in mutually opposed state and two tool heads capable of carrying out machining independently of each other with respective main spindles or carrying out combined machining simultaneously with at least one main spindle.
Among machine tools of this character known heretofore, there has been a machine having two main spindles on which are mounted respective chucks for holding workpieces, and which are disposed in mutually opposed coaxial positions on a common axis of rotation, one of the main spindles being capable of undergoing feeding movement relative to the other in the direction of their axis of rotation. Further, two tool heads, each capable of undergoing relative feeding movements in the direction of the rotational axis of the main spindles and in the direction perpendicular thereto to perform machining in the machining region encompassing the axis of rotation of the main spindles are also provided in this machine.
Such a machine is disclosed in U.S. Pat. No. 4,457,193, dated July 3, 1984, entitled "Machine-Tool Comprising Two Opposed Coaxial Spindles", issued to Maurice Matthey. In the relationship between the main spindles and the tool heads in the arrangement of this machine, the axes of rotation of the two main spindles are on a common line, and, in the case of simultaneous machining by the two tool heads with respective main spindles, there arise problems such as interference of tools and limitation of scope of machining.
For example, in turning work, when internal machining is carried out simultaneously with the two main spindles or in a case such as that wherein, during primary machining with one of the main spindles, the workpiece machined by that main spindle is transferred via conveying means to the other main spindle, or wherein one of the main spindles transfers the workpiece by undergoing a feeding movement relative to the other main spindle, and secondary back surface or reverse machining of the workpiece is carried out, the two tool heads must be maintained in such a mutual positional relation that, with mutual clearance on the axis of rotation of the main spindles, there will be no interference mutually between the tools.
In such a case, there is a great tendency for the two tool heads to undergo relative feeding movement in mutually back-to-back relation in the machining region encompassing the axis of rotation of the main spindles, and the moving distance of the slide in the longitudinal direction becomes great, whereby the machine tends to become large. Furthermore, in order to prevent mutual interference of the tools, the swinging arcs of the tool holders unavoidably become smaller, and the scope of machining with respect to the machine functional capacity becomes narrow. Still another problem is that, also in avoiding tool interference, it is necessary to prepare a program based on the machining processes of the workpieces of the respective main spindles. Such a program gives rise to complications, and at the same time, the editing requires considerable work and time.